Comparison of relaxation responses of detrusor strips from neuropathic and control patients

OBJECTIVES: To confirm the existence of relaxation responses to electrical-field stimulation in strips of human detrusor, and to compare these responses in strips from control subjects with those in strips from a group of neuropathic patients exhibiting hyperreflexia. PATIENTS AND METHODS: Detrusor specimens were obtained at operation from a group of control patients, and from a group of patients with neuropathy (mainly spina bifida) and a history of hyper-reflexia. Muscle strips were prepared from these, mounted in organ baths, and contracted by exposure to a modified Krebs' solution containing 26 mM KCl and atropine. Relaxation responses were induced by an electrical-field stimulation (50 V, 90 microsecond pulses at 2-16 Hz for 10 s). RESULTS: Of 29 strips, 20 (69%) from control patients showed relaxations, compared with 17 of 28 strips (61%) from neuropathic patients (P > 0.1). The maximum relaxation response in the control strips was 49 +/- 5.6% (mean +/- SEM) of the maximum relaxation induced by isobutyl methylxanthine, compared with 43 +/- 4.8% in the strips from neuropathic patients (P > 0.1). The maximum response occurred at similar frequencies (4 or 8 Hz) in the two groups. The relaxations were reduced by the inhibitor of nitric oxide synthase, N-nitro L-arginine methyl ester (0.1 mM, P < 0.05), but were not affected by guanethidine (50 microM) or tetrodotoxin (0.5 microM). CONCLUSION: These results confirm the existence of field stimulation-induced relaxation in human detrusor, but suggest that hyper-reflexia in the neuropathic bladder cannot be accounted for by any deficiency in this response.